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991.
Luciana Moreira Chedier Selma Ribeiro de Paiva Jos Luiz Mazzei da Costa Maria Raquel Figueiredo Maria Auxiliadora Coelho Kaplan 《Journal of separation science》1999,22(9):527-530
The family Guttiferae belongs to the superorder Theiflorae, order Theales and according to Dahlgren's system of classification, it is equivalent to Hypericaceae (=Clusiaceae) [1]. This family consists of 49 genera encompassing over 1000 species of wide distribution in the tropics as shrubs and trees [2]. Plants of the genus Clusia have been used in folk medicine for the treatment of different kind of illness such as: febrifuge, anti rheumatic, purgative, for stomach problems and, in Brazil, they are very commonly used to heal wounds [3]. The key of any study of material from natural sources is the availability of suitable separation methods for the isolation of pure products [4–6]. Tentatives for separations using chomatography on solid support phases were not very efficients in the fractionation of Clusia criuva Cambess methanolic/ethyl acetate extracts. However, the use of counter-current chromatography, an all liquid technique, showed advantages in comparison with the more traditional liquid-solid separation methods and even with HPLC. In this sense it was possible to isolate flavonoid glycosides from ethyl acetate extract of Clusia criuva, in a very short operation time. 相似文献
992.
E. Turiel P. Fernández C. Pérez-Conde A. M. Gutiérrez C. Cámara 《Fresenius' Journal of Analytical Chemistry》1999,365(8):658-662
An atrazine flow-through fluoroimmunosensor was developed, based on an oriented antibody covalently bound to Protein-A (Prot-A)
immobilized on Controlled Pore Glass (CPG). Atrazine was detected “in-situ” by placing the immobilized antibody in the optical
path of the flow cell. Immobilization of 30 μg of polyclonal anti-atrazine antibody on 0.5 g of Prot-A-CPG provided the highest
sensitivity. The effect of several solvents on the covalently immobilized antibodies regeneration was evaluated, the optimum
conditions being achieved by pumping 5% acetonitrile (pH = 3) at 0.15 mL/min for 100 s. The detection limit of the immunosensor
was 0.7 μg/L and the reproducibility was 2% and 4% for 5 μg/L and 40 μg/L, respectively, in the optimum working concentration
range (0.7–50 μg/L). This device allowed 12 samples per hour to be analyzed and had a life-time of 200 assays. Simazine and
desisopropylatrazine (DIA) were not cross-reactive, desethylatrazine (DEA) has a cross-reactivity of 8% and propazine and
prometryn of 44% and 27%, respectively. The immunosensor was applied to the determination of atrazine in tap and ground water
samples spiked at the ?10 and 30 μg/L concentration level.
Received: 30 April 1999 / Revised: 16 July 1999 / Accepted: 21 July 1999 相似文献
993.
A. Martín-Esteban P. Fernández C. Cámara G. N. Kramer E. A. Maier 《Fresenius' Journal of Analytical Chemistry》1999,363(7):632-640
The preparation of a certified reference material of polar pesticides in freeze-dried water is described. The pesticides
selected were atrazine, simazine, carbaryl, propanil, linuron, fenamiphos and permethrin which were added to 6000 litres of
tap water at 50–80 μg · L–1 (200–320 μg · L–1 for permethrin) level in presence of NaCl (2.5 g · L–1) prior lyophilization. After the freeze-drying process the residue was rehomogenized, filled into amber glass bottles and
stored at –20 °C, +4 °C and +20 °C. All pesticides were determined by HPLC/diode array detector, except permethrin which was
determined by GC/ECD. The results obtained for atrazine, simazine, carbaryl, propanil, linuron and fenamiphos showed no within-
or between-bottle inhomogeneity, however the material was non-homogeneous for permethrin and therefore this was withdrawn
from further studies. With respect to the stability for over one year, all pesticides were stable at –20 °C. At +4 °C all
pesticides were stable for at least 9 months and at +20 °C the stability was demonstrated only during the first month of storage.
The content (mass fractions) of atrazine, simazine, carbaryl, propanil and linuron in freeze-dried water (CRM 606) was certified
by an interlaboratory testing and a certification campaign.
Received: 7 September 1998 / Revised: 13 November 1998 / Accepted: 21 November 1998 相似文献
994.
A. J. Pardey M. Fernández M. Canestrari P. Baricelli E. Lujano C. Longo R. Sartori S. A. Moya 《Reaction Kinetics and Catalysis Letters》1999,67(2):325-331
Catalysts for the water gas shift reaction prepared from Rh(COD)(amine)2 PF6 (COD=1,5-cyclooctadiene, amine=4-picoline, 3-picoline, 2-picoline, pyridine, 3,5-lutidine or 2,6-lutidine) immobilized on
poly(4-vinylpyridine) in contact with 80% aqueoux 2-ethoxyethanol for 1×10−4 mol Rh/0.5 g of polymer, P(CO)=0.9 atm at 100 °C, are described. The role of the coordinated amine effect on the catalytic
activity was investigated. 相似文献
995.
Ivo Paulo Luis Costa Abel Rodrigues Sofia Orikov Sandro Matos Diogo Gonalves Ana Raquel Gonalves Luciana Silva Salom Vieira Joo Carlos Bordado Rui Galhano dos Santos 《Molecules (Basel, Switzerland)》2022,27(1)
Liquefaction of biomass delivers a liquid bio-oil with relevant chemical and energetic applications. In this study we coupled it with short rotation coppice (SRC) intensively managed poplar cultivations aimed at biomass production while safeguarding environmental principles of soil quality and biodiversity. We carried out acid-catalyzed liquefaction, at 160 °C and atmospheric pressure, with eight poplar clones from SRC cultivations. The bio-oil yields were high, ranging between 70.7 and 81.5%. Average gains of bio-oil, by comparison of raw biomasses, in elementary carbon and hydrogen and high heating, were 25.6, 67, and 74%, respectively. Loss of oxygen and O/C ratios averaged 38 and 51%, respectively. Amounts of elementary carbon, oxygen, and hydrogen in bio-oil were 65, 26, and 8.7%, and HHV averaged 30.5 MJkg−1. Correlation analysis showed the interrelation between elementary carbon with HHV in bio-oil or with oxygen loss. Overall, from 55 correlations, 21 significant and high correlations among a set of 11 variables were found. Among the most relevant ones, the percentage of elementary carbon presented five significant correlations with the percentage of O (−0.980), percentage of C gain (0.902), percentage of O loss (0.973), HHV gain (0.917), and O/C loss (0.943). The amount of carbon is directly correlated with the amount of oxygen, conversely, the decrease in oxygen content increases the elementary carbon and hydrogen concentration, which leads to an improvement in HHV. HHV gain showed a strong positive dependence on the percentage of C (0.917) and percentage of C gain (0.943), while the elementary oxygen (−0.885) and its percentage of O loss (0.978) adversely affect the HHV gain. Consequently, the O/C loss (0.970) increases the HHV positively. van Krevelen’s analysis indicated that bio-oils are chemically compatible with liquid fossil fuels. FTIR-ATR evidenced the presence of derivatives of depolymerization of lignin and cellulose in raw biomasses in bio-oil. TGA/DTG confirmed the bio-oil burning aptitude by the high average 53% mass loss of volatiles associated with lowered peaking decomposition temperatures by 100 °C than raw biomasses. Overall, this research shows the potential of bio-oil from liquefaction of SRC biomasses for the contribution of renewable energy and chemical deliverables, and thereby, to a greener global economy. 相似文献
996.
M. Herrera-Zaldívar P. Fernández J. Piqueras V.V. Sukhoveyev V.A. Ivantsov Y.G. Shreter 《Applied Physics A: Materials Science & Processing》2000,71(1):55-58
Cathodoluminescence (CL) in the scanning electron microscope has been applied to study the luminescence emission of GaN single crystals grown by LPE methods. CL spectra show the presence of near band edge and of yellow emissions. The latter has been found to be mainly related to rows of hillocks formed at the growth steps. The origin of the yellow luminescence is discussed 相似文献
997.
Carmen Cruces-Blanco Antonio Segura Carretero Silvia Fernández Peinado Alberto Fernández Gutiérrez 《Mikrochimica acta》2000,134(1-2):107-111
A spectrofluorimetric method for the determination of methyl paraben based on derivatization with the labelling reagent dansyl
chloride (DNS-Cl), is presented. The effect of the reaction variables (pH, DNS-Cl concentration, temperature, reaction time)
and instrumental parameters, has been examined. A linear calibration graph in the ng/ml range has been established. The limit
of detection is 18 ng/ml with relative standard deviation less than 3%. The proposed method has been satisfactorily applied
to determination of the paraben in two pharmaceutical preparations.
Received May 25, 1999. Revision October 20, 1999. 相似文献
998.
A. Casado A. Fernández-Rueda T. Marshall J. Martínez R. Risco-Delgado E. Santos 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2000,11(3):465-472
The theory of parametric down conversion within the framework of the Wigner representation has been treated recently in a
series of papers using the standard model Hamiltonian. Here we take a more fundamental point of view studying the mechanism,
inside the crystal, for the production of the signal and idler beams. We begin from the evolution equations for the quantum
field operators, pass to the Wigner function and solve the resulting (Maxwell) equations with the use of the Green's function
method. We derive the time dependence of the coincidence detection probability as a function of the parameters of the nonlinear
crystal (in particular the length) the radius of the pumping beam, and the bandwidth of the filters in front of the detectors.
Received 24 January 2000 and Received in final form 24 March 2000 相似文献
999.
Carlos García Gorka Arana Nestor Etxebarria Luis A. Fernández 《Mikrochimica acta》2001,136(1-2):15-21
The analysis of mixtures of four phenolic compounds in an on-line system using UV-visible measurements with a fibre optic
probe is discussed in this work. The aim of this system is to provide accurate real time concentration profiles in order to
monitor the transport of phenols across a solid supported liquid membrane in both the feed and stripping phases. Different
calibration models are taking into account the pH of the solution, using experimental designs and the first derivative in
combination with different multivariate approaches like multiple linear regression (MLR), inverted least squares (ILS) and
partial least squares regression (PLS). The comparison of all these combinations is carried out by means of the predictive
residual error sum of squares (PRESS) evaluated from an independent set of spectra. From this comparison it is concluded that
a PLS model using first derivative spectra offers the most accurate and robust prediction in the permeation experiments. Additionally,
the stability of the model and the figures of merit obtained are also discussed.
Received July 22, 1999. Revision October 23, 2000. 相似文献
1000.
We present a (1+1)-dimensional fermionic quantum field theory with nonlocal couplings between currents. This model describes
an ensemble of spinless fermions interacting through forward, backward, and UMKLAPP scattering processes. We express the vacuum-to-vacuum
functional in terms of a nontrivial fermionic determinant. Using path-integral methods, we find a bosonic representation for
this determinant and an effective action depending on three scalar fields, of which two correspond to the physical collective
excitations and one is an auxiliary field, which can be integrated out using an approximation technique.
Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 118, No. 3, pp. 488–496, March, 1999. 相似文献